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RTP Payload Format for H.261 Video Streams
RFC 4587

Network Working Group                                            R. Even
Request for Comments: 4587                                       Polycom
Obsoletes: 2032                                              August 2006
Category: Standards Track

               RTP Payload Format for H.261 Video Streams

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This memo describes a scheme to packetize an H.261 video stream for
   transport using the Real-time Transport Protocol, RTP, with any of
   the underlying protocols that carry RTP.

   The memo also describes the syntax and semantics of the Session
   Description Protocol (SDP) parameters needed to support the H.261
   video codec.  A media type registration is included for this payload
   format.

   This specification obsoletes RFC 2032.

Even                        Standards Track                     [Page 1]
RFC 4587                H.261 RTP payload format             August 2006

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................3
   3. Structure of the Packet Stream ..................................3
      3.1. Overview of the ITU-T Recommendation H.261 .................3
      3.2. Considerations for Packetization ...........................4
   4. Specification of the Packetization Scheme .......................5
      4.1. Usage of RTP ...............................................5
      4.2. Recommendations for Operation with Hardware Codecs .........8
   5. Packet Loss Issues ..............................................9
   6. IANA Considerations ............................................10
      6.1. Media Type Registrations ..................................10
           6.1.1. Registration of MIME Media Type video/H261 .........10
      6.2. SDP Parameters ............................................12
           6.2.1. Usage with the SDP Offer Answer Model ..............12
   7. Backward Compatibility to RFC 2032 .............................13
      7.1. Optional H.261-Specific Control Packets ...................13
      7.2. New SDP Optional Parameters ...............................13
   8. Security Considerations ........................................14
   9. Acknowledgements ...............................................14
   10. Changes from RFC 2032 .........................................14
   11. References ....................................................15
      11.1. Normative References .....................................15
      11.2. Informative References ...................................15

Even                        Standards Track                     [Page 2]
RFC 4587                H.261 RTP payload format             August 2006

1.  Introduction

   ITU-T Recommendation H.261 [H261] specifies the encoding used by
   ITU-T-compliant video-conference codecs.  Although this encoding was
   originally specified for fixed-data rate Integrated Services Digital
   Network (ISDN) circuits, experiments [INRIA], [MICE] have shown that
   they can also be used over packet-switched networks, such as the
   Internet.

   The purpose of this memo is to specify the RTP payload format for
   encapsulating H.261 video streams in RTP [RFC3550].

   This document obsoletes RFC 2032 and updates the "video/h261" media
   type that was registered in RFC 3555.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119] and
   indicate requirement levels for compliant RTP implementations.

3.  Structure of the Packet Stream

3.1.  Overview of the ITU-T Recommendation H.261

   The H.261 coding is organized as a hierarchy of groupings.  The video
   stream is composed of a sequence of images, or frames, which are
   themselves organized as a set of Groups of Blocks (GOB).  Note that
   H.261 "pictures" are referred to as "frames" in this document.  Each
   GOB holds a set of 3 lines of 11 macro blocks (MB).  Each MB carries

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